U.S. patent application number 16/986203 was filed with the patent office on 2021-02-11 for plate-shaped, chemically prestressed or chemically prestressable glass articles, and methods of producing.
This patent application is currently assigned to SCHOTT AG. The applicant listed for this patent is SCHOTT AG. Invention is credited to Jochen Alkemper, Oliver Hochrein, Sebastian Leukel, Thomas Seuthe, Julia Wei huhn.
Application Number | 20210039990 16/986203 |
Document ID | / |
Family ID | 1000005050790 |
Filed Date | 2021-02-11 |
![](/patent/app/20210039990/US20210039990A1-20210211-D00000.png)
![](/patent/app/20210039990/US20210039990A1-20210211-D00001.png)
United States Patent
Application |
20210039990 |
Kind Code |
A1 |
Leukel; Sebastian ; et
al. |
February 11, 2021 |
PLATE-SHAPED, CHEMICALLY PRESTRESSED OR CHEMICALLY PRESTRESSABLE
GLASS ARTICLES, AND METHODS OF PRODUCING
Abstract
A chemically prestressed or chemically prestressable,
plate-shaped or disc-shaped glass article is provided. The glass
article includes a glass with a composition of Al.sub.2O.sub.3,
SiO.sub.2, Na.sub.2O, and Li.sub.2O and a prestressing or a
prestressability in relation to the weight percent of Na.sub.2O of
at least 250 MPa/g Na.sub.2O in 100 g of glass. The Na.sub.2O is
present in a weight percent between at least 0.8 and at most 6.
Inventors: |
Leukel; Sebastian; (Mainz,
DE) ; Seuthe; Thomas; (Jena, DE) ; Alkemper;
Jochen; (Klein-Winternheim, DE) ; Wei huhn;
Julia; (Mainz, DE) ; Hochrein; Oliver; (Mainz,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCHOTT AG |
Mainz |
|
DE |
|
|
Assignee: |
SCHOTT AG
Mainz
DE
|
Family ID: |
1000005050790 |
Appl. No.: |
16/986203 |
Filed: |
August 5, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03C 3/097 20130101;
C03C 2204/00 20130101; C03C 3/085 20130101; C03C 4/18 20130101;
C03C 21/002 20130101; C03C 3/087 20130101; C03C 3/091 20130101;
C03C 3/083 20130101; C03C 3/093 20130101 |
International
Class: |
C03C 21/00 20060101
C03C021/00; C03C 4/18 20060101 C03C004/18; C03C 3/083 20060101
C03C003/083; C03C 3/085 20060101 C03C003/085; C03C 3/087 20060101
C03C003/087; C03C 3/091 20060101 C03C003/091; C03C 3/093 20060101
C03C003/093; C03C 3/097 20060101 C03C003/097 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 5, 2019 |
DE |
10 2019 121 143.3 |
Claims
1. A chemically prestressed or chemically prestressable,
plate-shaped or disc-shaped glass article, comprising: a glass with
a composition comprising Al.sub.2O.sub.3, SiO.sub.2, Na.sub.2O, and
Li.sub.2O, wherein the Na.sub.2O is present in a weight percent
between at least 0.8 and at most 6; and a prestressing or a
prestressability in relation to the weight percent of Na.sub.2O of
at least 250 MPa/g Na.sub.2O in 100 g of glass.
2. The glass article of claim 1, wherein the Na.sub.2O is at most
4.5 wt %.
3. The glass article of claim 1, wherein the prestressing or
prestressability is at most 1000 MPa/g Na.sub.2O.
4. The glass article of claim 1, wherein the prestressing or
prestressability is at most 1500 MPa/g Na.sub.2O.
5. The glass article of claim 1, wherein the composition comprises
at least 57 wt % SiO.sub.2 and at most 69 wt % SiO.sub.2.
6. The glass article of claim 1, wherein the composition comprises
at least 17 wt % Al.sub.2O.sub.3 and at most 24 wt %
Al.sub.2O.sub.3.
7. The glass article of claim 1, wherein the composition comprises
a sum of content of SiO.sub.2 and Al.sub.2O.sub.3 that is no more
than 92 wt %.
8. The glass article of claim 1, wherein the composition comprises
a total content of network formers that is at most 92 wt %.
9. The glass article of claim 1, wherein the composition comprises
a total content of alkali oxides that is at least 4 wt % and at
most 12 wt %.
10. The glass article of claim 1, wherein the composition comprises
at least 3 wt % Li.sub.2O and at most 5.5 wt % Li.sub.2O.
11. The glass article of claim 1, wherein the composition comprises
at most 7 wt % B.sub.2O.sub.3.
12. The glass article of claim 1, wherein the composition
comprises, in wt %: TABLE-US-00004 SiO.sub.2 57 to 69,
Al.sub.2O.sub.3 17 to 25, Li.sub.2O 3 to 5.5, Na.sub.2O 0.8 to 6,
and a sum of a content of Al.sub.2O.sub.3 and SiO.sub.2 lies
between at least 75 and at most 92.
13. The glass article of claim 12, wherein the composition
comprises: TABLE-US-00005 SiO.sub.2 61 to 69, Al.sub.2O.sub.3 17 to
21, Li.sub.2O 3.5 to 5.5, and Na.sub.2O 0.8 to 6.
14. The glass article of claim 1, further comprising a thickness
between at least 0.4 mm and at most 3 mm.
15. The glass article of claim 1, further comprising an acid
resistance determined as a half weight loss per unit area in
mg/dm.sup.2in a test in accordance with DIN 12116 that is no more
than 15 mg/dm.sup.2.
16. The glass article of claim 1, wherein the glass article is
configured for a use selected from a group consisting of a cover
panel, a cover panel for a consumer electronic device, a cover
panel for a display device, a cover panel for a computer monitor, a
cover panel for a measurement device, a cover panel for a
television, a cover panel for a mobile device, a cover panel for a
mobile terminal, a cover panel for a mobile data processing device,
a cover panel for a mobile phone, a cover panel for a mobile
computer, a cover panel for a palm top, a cover panel for a laptop,
a cover panel for a tablet computer, a cover panel for a wearable
device, a cover panel for a portable watch, a cover panel for a
time measuring device, a protective glass for a machine, a glazing
for a high-speed train, safety glass, an automobile glazing, a
diving watch, a submarine, and a cover panel for an
explosion-protected device.
17. A glass comprising a composition, in wt. %, of: TABLE-US-00006
SiO.sub.2 57 to 69, Al.sub.2O.sub.3 17 to 25, B.sub.2O.sub.3 0 to
7, Li.sub.2O 3 to 5.5, Na.sub.2O 0.8 to 6, and a sum of a content
of Al.sub.2O.sub.3 and SiO.sub.2 lies between at least 75 and at
most 92.
18. The glass of claim 17, wherein the composition comprises:
TABLE-US-00007 SiO.sub.2 61 to 67, Al.sub.2O.sub.3 17 to 21,
B.sub.2O.sub.3 0 to 4.5, Li.sub.2O 3.5 to 5.5, and Na.sub.2O 0.8 to
4.5.
19. The glass of claim 17, wherein the glass is a chemically
prestressed, plate-shaped or disc-shaped glass article.
20. A method for producing a glass article, comprising: providing a
glass comprising a composition, in wt. %, of: SiO.sub.2 57 to 69,
Al.sub.2O.sub.3 17 to 25, B.sub.2O.sub.3 0 to 7, Li.sub.2O 3 to
5.5, Na.sub.2O 0.8 to 6, and a sum of a content of Al.sub.2O.sub.3
and SiO.sub.2 lies between at least 75 and at most 92; and
conducting a first ion exchange between the glass and a first
exchange bath comprising between at least 20 wt. % and up to 100
wt. % of sodium nitrate for a duration of at least 2 hours and at
most 24 hours at a temperature of the first exchange bath of
between at least 380.degree. C. and at most 440.degree. C.
21. The method of claim 20, further comprising conducting a second
ion exchange in a second exchange bath comprising between 0 wt. %
and 10 wt. % of sodium nitrate for a duration of at least one hour
and at most 6 hours at a temperature of the second exchange bath of
at least 380.degree. C. and at most 440.degree. C.
22. The method of claim 21, further comprising adding the sodium
nitrate to the first exchange bath to provide the second exchange
bath.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit under 35 USC .sctn. 119 of
German Application No. 10 2019 121 143.3 filed Aug. 5, 2019, the
entire contents of which are incorporated herein by reference.
BACKGROUND
1. Field of the Invention
[0002] The invention relates to a plate-shaped, chemically
prestressed or at least chemically prestressable glass article and
to a method for the production thereof. Furthermore, the present
disclosure also relates to a glass composition.
2. Description of Related Art
[0003] Plate-shaped prestressed, in particular chemically
prestressed and especially chemically highly prestressed glass
articles find use, in particular, as so-called protective glasses
(or covers or cover glasses) for mobile devices such as smartphones
or tablet computers. In comparison to covers made of transparent
plastics, these protective glasses are, in particular, more
scratch-resistant, but they do also have a greater weight.
[0004] Only chemically prestressed, plate-shaped glass articles
find a use as protective glasses for mobile devices, since these
glass articles are again more resistant toward mechanical wear
loads; that is, they exhibit the resistance to wear required for
the application in question. In the context of the present
disclosure, wear resistance is understood to mean the resistance of
a product (or article, such as a glass article or a glass product)
toward mechanical loads, in particular toward abrasive loads,
scratch loads, or impact loads. The term wear resistance or, in
short, strength, is thus used in the context of the present
disclosure as a general term for the mechanical resistance of a
product or article. Special forms of wear resistance or, in short,
strength, are, for example, the scratch resistance, the flexural
strength, and the impact strength and it has been found that these
loads can also be linked to one another and such links are of
special relevance especially in practical application. Such
practical loads are, for example, impact on a rough surface, in
particular in an installed state.
[0005] Besides the requirements placed on a good wear resistance,
however, the plate-shaped glass article should also meet further
requirements. In particular, the glass comprised by the glass
article should be easy to produce; that is, it should be amenable
to a melting process followed by a hot shaping process, during
which devitrification should preferably not occur. The chemical
resistance of the glass article is also of relevance, in particular
its resistance to acids. This is to be regarded, in particular,
against the background that, although a good resistance of the
final product is necessary, a good prestressability in an ion
exchange process also needs to be given, on the other hand.
[0006] Chemically prestressable glasses and/or chemically
prestressable or chemically prestressed glass articles and/or
methods for producing such articles are known.
[0007] Chemically prestressable glasses can be differentiated into
so-called aluminum silicate glasses (also referred to as AS
glasses, alumosilicate glasses, or aluminosilicate glasses), which
comprise as components, in particular, Al.sub.2O.sub.3 and
SiO.sub.2 as well as alkali oxides, except for lithium oxide
Li.sub.2O, as well as lithium aluminum silicate glasses (also
referred to as LAS glasses, lithium alumosilicate glasses, or
lithium aluminosilicate glasses), which, furthermore, additionally
comprise Li.sub.2O as a component.
[0008] These glasses are designed in such a way that they can be
chemically prestressed. A glass that can be chemically prestressed
is understood in the context of the present disclosure to mean a
glass that is amenable to an ion exchange process. In such a
process, ions of alkali metals are exchanged in a surface layer of
a glass, such as, for example, a glass plate or disc. This occurs
in such a way that a zone of compressive stress is then built up in
the surface layer, this being brought about by the exchange of ions
having small radii with ions having larger radii. For this purpose,
the glass article is immersed in a so-called ion exchange bath,
such as, for example, a molten salt, where the ion exchange bath
comprises the ions having the larger ionic radii, in particular
potassium ions and/or sodium ions, so that these ions migrate into
the surface layer of the glass article. In exchange therefor, ions
having smaller ionic radii, in particular lithium ions and/or
sodium ions, migrate out of the surface layer of the glass article
into the ion exchange bath.
[0009] In this way, a zone of compressive stress is formed. This
zone of compressive stress can be described by the characterizing
values of compressive stress, which is abbreviated as "CS," and the
depth of compressive stress, which is also referred to as "depth of
layer" or, abbreviated, "DoL." This depth of compressive stress DoL
is well known to the person skilled in the art and, in the context
of the present disclosure, refers to the depth at which the stress
curve has the stress zero-crossing. Alternatively or additionally,
this thickness DoL can be determined by means of an optical
zero-crossing stress measurement method, such as, for example, by
means of a measuring instrument with the trade name FSM-6000 or SLP
1000.
[0010] It is also possible by means of this measuring instrument to
measure the compressive stress of the surface of aluminosilicate
glasses as well as the maximum compressive stress CS of a plate or
of a plate-shaped glass article.
[0011] The known glasses of the prior art hereby generally have a
high content of alkali oxides as components. This has hitherto been
regarded as being necessary in order to make it possible to design
a glass article to be prestressable to high compressive stresses.
At the same time, a high content of alkali oxides leads to a
lowering of the melt temperature.
[0012] However, there are conflicting goals here. Thus, although
the prestressable glasses of the prior art can, as a rule, be
readily melted and are amenable to an ion exchange, it has been
found that, on the one hand, long immersion times are necessary in
order to create the desired high compressive prestresses at the
surface of the glass article. On the other hand, a high content of
alkali oxides is unfavorable, in principle, in regard to the
chemical resistance, such as, for example, the resistance of the
glass article to hydrolysis and/or to acids.
[0013] Therefore, there is a need for plate-shaped glass articles
that are designed to be chemically highly prestressable and here,
at the same time, to be readily melted and that exhibit an acid
resistance. In a corresponding way, there is a need for chemically
prestressed, plate-shaped glass articles with high compressive
prestress and preferably, at the same time, a good resistance to
acids.
SUMMARY
[0014] The object of the invention consists in providing
plate-shaped glass articles, in particular chemically prestressable
or chemically prestressed plate-shaped glass articles, which at
least alleviate the drawbacks of the prior art.
[0015] In accordance with a first aspect, the present disclosure
thus relates to a chemically prestressed or at least chemically
prestressable, plate-shaped glass article that comprises a glass
with a composition comprising Al.sub.2O.sub.3, SiO.sub.2,
Na.sub.2O, and preferably Li.sub.2O and having preferably at least
one of the following features: The glass comprises at most 6 wt %
Na.sub.2O, preferably at most 5.5 wt % Na.sub.2O, especially
preferably at most 4.5 wt % Na.sub.2O, and preferably at least 0.8
wt % Na2O and/or The glass article has a prestress or at least a
prestressability, CS, in relation to the weight percent of
Na.sub.2O in the glass article, of at least 250 MPa/g Na.sub.2O in
relation to an amount of 100 g of glass. Preferably, the
prestressability is at most 1500 MPa/g Na.sub.2O, especially
preferably at most 1000 MPa/g Na.sub.2O, in relation to an amount
of 100 g of glass.
[0016] Such a design of a glass article has a number of
advantages.
[0017] As a result of the design of the glass article so that it
comprises a glass with a composition comprising Al.sub.2O.sub.3,
SiO.sub.2, and Na.sub.2O, the plate-shaped glass article is
designed, first of all, to be chemically prestressable, since what
is involved here in the case of the glass comprising the glass
article is an AS glass or even a LAS glass. Preferably, namely, the
glass article is designed such that the glass comprising the glass
article comprises Li.sub.2O. As is known, such AS and LAS glasses
are amenable to a chemical hardening or to a chemical prestressing
by way of an ion exchange.
[0018] In this embodiment, the glass comprises at most 6 wt %,
preferably at most 5.5 wt % Na.sub.2O, especially preferred also
only at most 4.5 wt % Na.sub.2O. A low content of the alkali oxide
Na.sub.2O is especially advantageous in regard to the resistance to
acids, since alkali oxides can be leached out of a glass, whereby,
due to the smaller field strength of the sodium ion, in comparison
to a lithium ion, for example, it is more readily leachable.
Therefore, the Na.sub.2O content is limited.
[0019] The low content in the glass and, in a corresponding way, in
the glass article comprising the glass is advantageous against the
background of producing the glass article, in particular during
chemical prestressing. Since the glass comprises little Na.sub.2O,
there is also only little poisoning of the exchange bath due to
sodium ions migrating out of the glass into the exchange bath. This
is therefore advantageous in regard to the economy of the
production method.
[0020] However, the glass or the glass article comprising the glass
has a minimum content of Na.sub.2O. This is necessary in order for
the glass to be amenable to an ion exchange and, in particular, to
a so-called potassium exchange. Moreover, in this way, the
meltability of the glass is improved. Preferably, the glass or the
glass article comprises at least 0.8 wt % Na.sub.2O.
[0021] It is surprising, however, that, with such a low Na.sub.2O
content of at least only 0.8 wt %, nonetheless good compressive
prestresses can be achieved. In particular, on account of the
potassium exchange, compressive prestresses (CS) of at least 600
MPa and of up to 1000 MPa are achieved.
[0022] Alternatively or additionally, the glass article is designed
in such a way that it has a prestress or at least a
prestressability, in relation to the weight percent of Na.sub.2O in
the glass or in the glass article, of at least 250 MPa/g Na.sub.2O
in relation to an amount of 100 g of glass. Preferably, the
prestressability is at most 1500 MPa/g Na.sub.2O, especially
preferred at most 1000 MPa/g Na.sub.2O, in relation to an amount of
100 g of glass.
[0023] In other words, the glass or the glass article is designed
in this case in such a way that it has a large stress in relation
to the sodium oxide comprised by the glass or glass article.
BRIEF DESCRIPTION OF THE FIGURES
[0024] The invention will be explained in detail below on the basis
of drawings. Shown are:
[0025] FIG. 1 is a schematic and not dimensionally accurate
illustration of a glass article in accordance with the presently
disclosed embodiments;
[0026] FIG. 2 is a schematic and not dimensionally accurate
sectional image through a glass article in accordance with the
presently disclosed embodiments.
DETAILED DESCRIPTION
[0027] In the context of the present disclosure, prestressability
is understood to mean the ability of a glass or of a glass article
to be highly prestressed, in particular the ability of taking up
and storing stresses that are introduced. In the context of the
present disclosure, high prestresses refer to prestresses that are
at least 400 MPa.
[0028] It has hitherto been assumed that a large absolute amount of
alkali ions comprised by the glass or by the glass article is
necessary in order for the glass or for the glass article
comprising the glass to be readily prestressable or in order to
achieve a high chemical prestress of the glass article of at least
400 MPa or preferably at least 600 MPa, in particular for glass
thicknesses of at least 0.4 mm and of up to 3 mm. Surprisingly,
however, it has been found that, with only low contents of the
alkali ion to be exchanged, it is possible to ensure good
prestressabilities.
[0029] Two aspects seem hereby worthy of note:
[0030] Thus, a low absolute content of the alkali ion that is to be
exchanged, that is, in particular the sodium ion in this case, is
still able to lead to an adequate prestress and even to a high
prestress of at least 600 MPa and of even up to 1000 MPa, in
particular for glass articles with glass thicknesses from at least
0.4 mm up to 3 mm, when the alkali ions, in particular the sodium
ions, are readily amenable to an ion exchange. The first aspect
thus relates to the exchangeability of the alkali ions comprised by
the glass or by the glass article. The inventors are of the opinion
that prestresses even higher than 1000 MPa can be achieved.
[0031] Alternatively or additionally, however, the prestressability
of the glass matrix is also significant. This means that a high
exchangeability of the alkali ions that are to be exchanged is not
or not only or not solely significant, but rather also the ability
of the glass matrix to build up and/or to store a prestress is
significant.
[0032] If both prerequisites are met, that is, when a large
proportion of the alkali ions comprised by the glass is readily
amenable to an exchange and, at the same time, the glass matrix is
designed to build up and/or store a high prestress, even a possibly
absolutely low proportion of alkali ions to be exchanged may be
sufficient in order to obtain, nonetheless, a chemically highly
prestressable or chemically prestressed glass article.
[0033] In the context of the present disclosure, the following
definitions apply:
[0034] An exchange bath is understood to mean a molten salt that is
employed in an ion exchange method for a glass or for a glass
article. In the context of the present disclosure, the terms
exchange bath and ion exchange bath are used synonymously.
[0035] As a rule, salts of technical-grade purity are used for
exchange baths. This means that, in spite of the use of solely
sodium nitrate, for example, as the starting material for an
exchange bath, certain contaminants are still present in the
exchange bath. The exchange bath is here a melt of a salt, such as,
for example, sodium nitrate, or a melt of a mixture of salts, such
as, for example, a mixture of a sodium salt and a potassium salt.
In this case, the composition of the exchange bath is present in
the form that relates to the nominal composition of the exchange
bath without taking into consideration possibly present
contaminants. Therefore, in the context of the present disclosure,
insofar as a 100% sodium nitrate melt is indicated, this therefore
means that, as raw material, solely sodium nitrate was used.
However, the actual content of sodium nitrate in the exchange bath
can deviate from this and, as a rule, does so, because, in
particular, technical-grade raw materials have a certain proportion
of contaminants. However, as a rule, these contaminants constitute
less than 5 wt % in relation to the total weight of the exchange
bath, in particular less than 1 wt %.
[0036] In a corresponding way, in the case of exchange baths that
have a mixture of different salts, the nominal contents of these
salts are presented without taking into consideration technically
caused contaminants of the starting materials. An exchange bath
containing 90 wt % KNO.sub.3 and 10 wt % NaNO.sub.3 can therefore
also still have small amounts of contaminants, which, however, are
due to raw materials and, as a rule, should constitute less than 5
wt % in relation to the total weight of the exchange bath, in
particular less than 1 wt %.
[0037] Furthermore, the composition of the exchange bath also
changes in the course of the ion exchange, because, owing to the
progressing ion exchange, particularly lithium ions migrate out of
the glass or out of the glass article into the exchange bath.
However, such a change in the composition of the exchange bath due
to aging is also not taken into consideration in the present case,
insofar as it is not explicitly stated otherwise. Instead, in the
context of the present disclosure, the nominal original composition
is taken into account in stating the composition of an exchange
bath.
[0038] A stress profile is understood in the context of the present
disclosure to mean the plot in a diagram of the stress in a glass
article, such as, for example, in a glass plate, versus the
thickness of the glass in question. Insofar as, in the context of
the present disclosure, a compressive stress profile is addressed,
this is understood here to mean the part of a stress profile in
which the stress takes on positive values, that is, is greater than
zero. In contrast, tensile stress has a negative sign. What is
involved thereby is the definition of the sign of the stress as it
is conventionally used by the person skilled in the art, that is,
the developer of prestressed protective glasses, in regard to the
sign of the stress. This differs especially from the usual
reference to the compressive stress as negative and the tensile
stress as positive, such as, for example, as conventionally assumed
in physics. In the context of the present disclosure, however,
recourse is made here, as discussed, to the definition of stresses
as conventionally used in the glass industry.
[0039] A combined compressive stress profile is understood in the
context of the present disclosure to mean a compressive stress
profile for which the compressive stress in the corresponding
article, such as a glass article, is combined from at least two
subregions.
[0040] The compressive stress stored in a prestressed glass article
is obtained by integration of the compressive stress over the
thickness of the glass article. In the context of the present
disclosure, this integral is referred to as the compressive stress
integral.
[0041] The tensile stress stored in a prestressed glass article is
obtained by the integration of the tensile stress over the
thickness of the glass article. In the context of the present
disclosure, this integral is referred to as the tensile stress
integral. In the context of the present disclosure, the terms:
stored tensile stress and tensile stress integral are therefore
also used synonymously.
[0042] A plate-shaped glass article is understood in the context of
the present disclosure to mean a glass article for which the
lateral dimension in one spatial direction is at least an order of
magnitude less than that in the two other spatial directions,
whereby these spatial directions are given with respect to a
Cartesian coordinate system, in which these spatial directions
extend perpendicular to one another and the thickness in the
direction of the normal to the largest or main surface is hereby
measured from the one main surface to the other main surface.
[0043] Because the thickness is at least an order of magnitude less
than the width and length of the glass article, the width and
length can thereby be of the same order of magnitude. However, it
is also possible that the length is again markedly greater than the
width of the glass article. In the sense of the present disclosure,
plate-shaped glass articles can therefore comprise a glass
ribbon.
[0044] In the sense of the present disclosure, a glass is
understood to mean a material and a glass article is understood to
mean a product that is produced from the material glass and/or the
product comprising the material glass. In particular, a glass
article can be composed of glass or predominantly contain, that is,
up to at least 90 wt %, the material glass.
[0045] A chemical prestressing in the context of the present
disclosure is understood to mean a process in which a glass article
is immersed in a so-called exchange bath, resulting in an exchange
of ions. A potassium exchange is understood in the sense of the
present disclosure to mean that potassium ions migrate out of the
exchange bath into the glass article, in particular into the
surface of the glass article; that is, for example, they are
incorporated into the surface of the glass article, whereby, at the
same time, small alkali ions, such as, for example, sodium ions,
migrate out of the glass article into the exchange bath. A sodium
exchange is understood in a corresponding way to mean that sodium
ions migrate out of the exchange bath into the surface of the glass
article, whereas small ions, such as, for example, lithium ions,
migrate out of the glass article, in particular out of the surface
of the glass article, into the exchange bath. As already described,
this ion exchange results in the buildup of a zone of compressive
stress in the surface region of the glass article.
[0046] The maximum tensile stress is understood in the context of
the present disclosure to mean the minimum stress value in the
stress profile of a glass article.
[0047] A so-called "sharp impact" is understood in the context of
the present disclosure to mean a load for which the damage is
produced by a small sharp object or by a large number of such small
sharp objects. In other words, what is involved is therefore an
impact with one sharp object or a plurality of sharp objects, that
is, for example, with particles that have very small radii of
curvature or for which the angle of the tip of the particle is less
than 100.degree..
[0048] Insofar as, in the context of the present disclosure,
reference is made to the grit of an abrasive paper, this grit is
given taking into account and preferably in accord with DIN ISO
6344. This grit is oriented to mesh as a unit of measurement. The
larger the grit, the smaller are thereby the abrasive particles. In
the context of the present disclosure, the terms "grit 60" and
"#60"--here, for example, in relation to a so-called grit of
60--are used synonymously in referring to the grit. This obviously
applies in a corresponding way to other grits, such as, for
example, a 100 or 180 grit.
[0049] In the context of the present disclosure, the term field
strength of an ion is used in accordance with Dietzel. In
particular, this term is used in relation to an oxidic glass
matrix, with it being understood that this value can change
depending on the coordination number of the ion in question.
[0050] In regard to the terms network modifier and network former,
these terms are understood in accordance with Zachariasen.
[0051] In the context of the present disclosure, network formers
hereby refer, in particular, to SiO.sub.2, Al.sub.2O.sub.3,
B.sub.2O.sub.3, and P.sub.2O.sub.5.
[0052] Network modifiers refer, in particular, to alkali oxides and
alkaline earth oxides.
[0053] In particular, ZrO.sub.2 is referred to as a so-called
intermediate oxide.
[0054] A glass in accordance with embodiments of the present
disclosure or a plate-shaped, chemically prestressable or
chemically prestressed glass article in accordance with embodiments
of the present disclosure can also be designed, in particular, in
such a way that it comprises at most 6 wt % Na.sub.2O, preferably
at most 5.5 wt % Na.sub.2O, especially preferably at most 4.5 wt %
Na.sub.2O, where the minimum amount of Na.sub.2O is preferably at
least 0.8 wt %, where the glass article has a prestress or at least
a prestressability, in relation to the weight percent of Na.sub.2O
in the glass or in the glass article, of at least 250 MPa/g
Na.sub.2O in relation to an amount of 100 g of glass. Preferably,
the prestressability is at most 1500 MPa/g Na.sub.2O, especially
preferred at most 1000 MPa/g Na.sub.2O, in relation to an amount of
100 g of glass.
[0055] In this way, in an especially advantageous manner,
preferably a good resistance of the glass or glass article is
obtained, whereby the glass article is formed in a chemically
highly prestressed manner or in a chemically highly prestressable
manner.
[0056] The reason is not yet entirely understood why, with even an
only very small content of Na.sub.2O in the glass or in the glass
article, nonetheless a high chemical prestressing can be achieved
or is achieved. However, it is thought that the reason for this
lies in a targeted adjustment of the glass matrix or of the glass
network.
[0057] In accordance with an embodiment of the glass article, the
glass comprises the further composition percentages given in the
context of the present disclosure, but at least 57 wt % SiO.sub.2,
preferably at least 59 wt % SiO.sub.2, especially preferred at
least 61 wt % SiO.sub.2, and/or the glass comprises at most 69 wt %
SiO.sub.2, preferably at most 67 wt %.
[0058] As a glass constituent, SiO.sub.2 is a so-called network
former. A high proportion of SiO.sub.2 in a glass increases the
chemical resistance of the glass, in particular the resistance to
acids, and is therefore advantageous. It is also known that quartz
glass SiO.sub.2 forms a very rigid, three-dimensionally
cross-linked glass network. In accordance with one embodiment of
the glass or of the glass article, therefore, the content of
SiO.sub.2, with the otherwise further presently disclosed
constituents of the composition, is at least 57 wt %, preferably
even at least 59 wt% SiO.sub.2, and especially preferred at least
61 wt % SiO.sub.2. However, too high a content of SiO.sub.2 results
in the glass being only poorly meltable.
[0059] For this reason, in accordance with the presently disclosed
embodiments, the content SiO.sub.2 in the glass is limited and is
at most 69 wt %, preferably at most 67 wt %.
[0060] As a glass constituent, Al.sub.2O.sub.3, like SiO.sub.2, is
a network former. A minimum content of Al.sub.2O.sub.3 within the
above-mentioned limits in the glasses and in the glass articles in
accordance with embodiments is advantageous, since the addition of
Al.sub.2O.sub.3 results in a reduction in the number of
non-bridging oxygens in an alkali-containing silicate glass, so
that, in spite of a certain content of a glass, a rigid network can
be obtained. It has been found that the formation of a relatively
rigid glass network is favorable for the prestressability of an
alkali-containing glass.
[0061] However, in accordance with one embodiment, the content of
Al.sub.2O.sub.3 in the glass or in the glass article is also
limited along with the further constituents of the composition
otherwise given in the context of the present disclosure, since, in
too large amounts, Al.sub.2O.sub.3 leads to a decline in the
resistance of the glass to acids in particular. Therefore, in
accordance with this embodiment, the content of Al.sub.2O.sub.3 in
the glass or in the glass article is preferably at least 17 wt %
and/or at most 25 wt %, preferably at most 24 wt % and especially
preferred at most 21 wt %.
[0062] It has been found overall that an especially good
prestressability of the glass or of the glass article or an
especially high chemical prestressing, in particular in relation to
the weight percent of Na.sub.2O in the glass or in the glass
article, can be obtained by way of a high content of network
formers in the glass or in the glass article, in particular by way
of a high content of the network formers SiO.sub.2 and
Al.sub.2O.sub.3 in the glass. In accordance with preferred
embodiments of the glass or of the glass article, the content of
network formers in the glass or in the glass article is, in each
case, at least 82 wt % and/or is equal to a sum of the content of
Al.sub.2O.sub.3 and SiO.sub.2 in the glass or in the glass article
of at least 75 wt %. This high content of network formers in the
glass or in the glass article, in particular a high content of the
network formers SiO.sub.2 and Al.sub.2O.sub.3, evidently results,
namely, in a glass structure that can store stresses in an
especially good manner. Although the content of Al.sub.2O.sub.3 in
the glass reduces the number of the non-bridging oxygens in the
glass network, nonetheless, in this case, a still adequate
resistance to acids is achieved. It is thought that the reason for
this lies in the interaction of the low absolute alkali content, in
particular the low sodium oxide content, with the overall high
content of network formers.
[0063] The prestressability can further be increased when the
content of network formers in the glass or in the glass article is
increased still further. However, the content of network formers in
the glass or in the glass article is preferably limited. In
accordance with one embodiment with the constituents of the
composition otherwise further presently disclosed, the sum of the
content of SiO.sub.2 and Al.sub.2O.sub.3 is no more than 92 wt %,
preferably no more than 90 wt %. Especially preferred, the total
content of network formers in the glass or in the glass article is
at most 92 wt %, most especially preferred at most 90 wt %. This is
advantageous, because, in this way, a glass that is still meltable
and consequently can be produced in an economical manner is
obtained.
[0064] As discussed above, it is an important aspect of the
prestressability that the alkali ions that are to be exchanged,
that is, in particular the sodium ions in this case, also are
present in an exchangeable form. However, this leads to conflicting
goals, because a high mobility of the alkali ions can also lead to
only a low chemical resistance, in particular to a low resistance
of the glass or of the glass article to acids. For this reason, the
content of alkali oxides in the glass or in the glass article
should not be too high.
[0065] In accordance with one embodiment, the total content of
alkali oxides in the glass and/or in the glass article is
preferably at least 4 wt % and at most 12 wt %, preferably at most
10 wt %.
[0066] Li.sub.2O is an optional component of the glass or of the
glass article in accordance with the presently disclosed
embodiments. Surprisingly, it has been found that, as a constituent
of a glass or of a glass article, Li.sub.2O also positively
influences the prestressability or the prestressing of the glass or
of the glass article even in the case when it itself does not take
part in the ion exchange, that is, when only a potassium exchange
occurs. This is ascribed to the fact that Li.sub.2O is a component
that supports the formation of a more rigid glass network, so that
a content of Li.sub.2O in the glass or in the glass article is
preferred in accordance with one embodiment of the glass or of the
glass article.
[0067] A content of Li.sub.2O in the glass or in the glass article
makes possible a mixed ion exchange, namely, in this case, an
exchange for sodium ions. This can be preferred, because, in this
way, it is possible to obtain chemically prestressable or
chemically prestressed glass articles that have especially
advantageous mechanical properties, such as, for example, for the
load of the chemically prestressed glass article in a so-called
set-drop test. In particular, the content in the glass or of the
glass article in accordance with a preferred embodiment can be at
least 3 wt %, preferably at least 3.5 wt %.
[0068] In accordance with a further embodiment of the glass article
or of the glass, the content of Li.sub.2O in the glass or in the
glass article is accordingly preferably at least 3 wt %, especially
preferred at least 3.5 wt %, and at most 5.5 wt %, preferably at
most 5.0 wt %. This is advantageous, because, in the case of higher
contents of Li.sub.2O in the glass or in the glass article, an
increased crystallization or an enhanced demixing of Li.sub.2O can
occur.
[0069] A further optional component of the glass or of the glass
article is B.sub.2O.sub.3. A certain content of B.sub.2O.sub.3 in
the glass can be advantageous, because this lowers the melting
point of the glass and therefore improves the meltability. As is
known, the component B.sub.2O.sub.3 also increases the scratch
resistance of a glass. Surprisingly, however, it has been found
that too high a content of B.sub.2O.sub.3 in the glass or in the
glass article diminishes the prestressability. In accordance with
one embodiment containing the otherwise presently disclosed
additional composition percentages, the content of B.sub.2O.sub.3
in the glass and/or in the glass article is therefore at most 7 wt
%, preferably at most 5 wt %, and especially preferred at most 4.5
wt %.
[0070] P.sub.2O.sub.5 is a further, optional component of the glass
and/or of the glass article in accordance with the presently
disclosed embodiments. A content of P.sub.2O.sub.5 in the glass
and/or in the glass article can be advantageous, since, as a glass
component, P.sub.2O.sub.5 can bring about the achievement of a
deeper prestressing in a shorter time. P.sub.2O.sub.5 can also be
advantageous, since, in this way, the exchange process can be
accelerated. However, a high content of P.sub.2O.sub.5 in the glass
is unfavorable, since P.sub.2O.sub.5 can attack the material of the
melting apparatus. The content of the glass and/or of the glass
article in accordance with embodiments should therefore be at most
3 wt %, preferably at most 2 wt % and especially preferred at most
1.7 wt %.
[0071] In accordance with another embodiment of the chemically
prestressed or chemically prestressable, plate-shaped glass
article, it comprises a glass comprising the following components
in wt %:
TABLE-US-00001 SiO.sub.2 57 to 69, preferably 59 to 69, especially
preferred 61 to 69, where the upper limit in each case can be
preferably 67, Al.sub.2O.sub.3 17 to 25, preferably 17 to 24,
especially preferred 17 to 21, B.sub.2O.sub.3 0 to 7, preferably 0
to 5, especially preferred 0 to 4.5, Li.sub.2O 3 to 5.5, preferably
3.5 to 5.5, especially preferred 3.5 to 5, Na.sub.2O 0.8 to 6,
preferably 0.8 to 5.5, or even more preferred from 0.8 to 4.5,
where preferably the sum of the content of Al.sub.2O.sub.3 and
SiO.sub.2, in relation to the given value in wt %, lies between at
least 75 and at most 92, preferably at most 90.
[0072] The combination of the components in the aforementioned way
provides a glass article that, surprisingly, is formed in an
especially highly chemically prestressable manner or is chemically
highly prestressed and thereby exhibits an adequate resistance to
acids with, at the same time, a good meltability. It is suspected
that the reason for this lies in the interaction of a small content
of an alkali having a low field strength in the glass or in the
glass article, namely, in this case, Na.sub.2O, with the
aforementioned content of network formers in the glass or in the
glass article. However, an adequate meltability can nonetheless be
achieved by way of the content of alkali oxides in the glass,
which, in this case, is at least 4 wt %. The high prestressability
of the glass or of the glass article in accordance with this
embodiment is presumably further increased by the content of
Li.sub.2O in the aforementioned limits, since, on account of the
high field strength of the lithium ion in comparison to other
network modifiers, the formation of a rigid glass network is
supported in an advantageous manner. At the same time, the lithium
ion is bound more strongly in the glass matrix than are other
alkali ions, which can also improve the resistance to acids.
[0073] In accordance with one embodiment of the plate-shaped glass
article, it has a thickness of between at least 0.4 mm and at most
3 mm, with the thickness preferably being at least 0.5 mm and/or
preferably being at most 2.0 mm, preferably at most 1.0 mm.
[0074] The glass article in accordance with the embodiments of the
present disclosure has a resistance to acids that is determined as
the half weight loss per unit area in mg/dm.sup.2 in a test based
on or in accordance with DIN 12116 and that is no more than 15
mg/dm.sup.2. The half weight loss per unit area for the glass
and/or for the glass article in accordance with embodiments is
therefore no more than 15 mg/dm.sup.2.
[0075] A second aspect of the present disclosure relates to a glass
article, in particular a glass article in accordance with an
embodiment in accordance with the present disclosure, in particular
in accordance with the first aspect of the present disclosure, that
is obtained in a method comprising the following steps: an optional
first ion exchange in an exchange bath comprising between at least
20 wt % and up to 100 wt % of a sodium salt, preferably sodium
nitrate NaNO.sub.3, is carried out for a period of time of at least
2 hours, preferably at least 4 hours, and at most 24 hours at a
temperature that lies between at least 380.degree. C. and at most
440.degree. C., whereby, optionally, a potassium salt, in
particular potassium nitrate, can be added to the exchange bath, in
particular such that the sum of the content of sodium salt and
potassium salt adds up to 100 wt %, as well as an ion exchange in
an exchange bath comprising between 0 wt % and 10 wt % of a sodium
salt, preferably sodium nitrate NaNO.sub.3, in relation to the
total amount of the salt, for a period of time of at least one hour
and at most 6 hours at a temperature of the exchange bath of at
least 380.degree. C. and at most 440.degree. C., whereby a
potassium salt is added to the exchange bath, in particular
preferably potassium nitrate KNO.sub.3, in particular such that the
sum of the content of sodium salt and potassium salt adds up to 100
wt %, as well as, optionally, one further exchange step or a
plurality of further exchange steps.
[0076] This means that, insofar as an ion exchange of sodium for
lithium takes place, that is, an ion exchange in an exchange bath
comprising between at least 20 wt % and up to 100 wt % of a sodium
salt, this occurs as the first step. However, this step is merely
optional, that is, need not necessarily be carried out.
[0077] Necessary, however, is the step of an ion exchange of
potassium for sodium, that is, in an exchange bath comprising
between 0 wt % and 10 wt % of a sodium salt, preferably sodium
nitrate NaNO.sub.3, in relation to the total amount of the salt,
whereby a potassium salt is added to the exchange bath, in
particular preferably potassium nitrate KNO.sub.3, in particular
such that the sum of the content of sodium salt and potassium salt
adds up to 100 wt %.
[0078] A third aspect of the present disclosure relates to a glass
comprising the following components in wt %:
TABLE-US-00002 SiO.sub.2 57 to 69, preferably 59 to 69, especially
preferred 61 to 69, where the upper limit in each case can be
preferably be 67, Al.sub.2O.sub.3 17 to 25, preferably 17 to 24,
especially preferred 17 to 21, B.sub.2O.sub.3 0 to 7, preferably 0
to 5, especially preferred 0 to 4.5, Li.sub.2O 3 to 5.5, preferably
3.5 to 5.5, especially preferred 3.5 to 5, Na.sub.2O 0.8 to 6,
preferably 0.8 to 5.5, especially preferred 0.8 to 4.5, where
preferably the sum of the content of Al.sub.2O.sub.3 and SiO.sub.2,
in relation to the given value in wt %, lies between at least 75
and at most 92, preferably at most 90, and/or where preferably the
total content of alkali oxides in the glass and/or in the glass
article is preferably at least 4 wt % and at most 12 wt %,
preferably at most 10 wt %.
[0079] As discussed above, what is involved here is a glass that
has an especially good prestressability, which can be understood,
for example, as a property of readily storing prestresses in the
glass network and/or as an ability of the glass to make possible,
together with, at the same time, a good resistance to acids, a good
exchangeability of the alkali ions that are present, in particular
of the sodium ions. In particular, this property of the glass can
also be expressed as a prestressing or at least as a
prestressability in relation to the weight percent of Na2O in the
glass or in the glass article, of at least 250 MPa/g Na.sub.2O in
relation to an amount of 100 g of glass. Preferably, the
prestressability is at most 1500 MPa/g Na.sub.2O, especially
preferred at most 1000 MPa/g Na.sub.2O, in relation to an amount of
100 g of glass.
[0080] The present disclosure relates, furthermore, to a method for
producing a glass article, preferably a glass article in accordance
with embodiments of the present disclosure, comprising the
steps:
[0081] an optional first ion exchange in an exchange bath
comprising between at least 20 wt % and up to 100 wt % of a sodium
salt, preferably sodium nitrate NaNO.sub.3, is carried out for a
period of time of at least 2 hours, preferably at least 4 hours,
and at most 24 hours at a temperature that lies between at least
380.degree. C. and at most 440.degree. C., whereby, optionally, a
potassium salt, in particular potassium nitrate, can be added to
the exchange bath, in particular such that the sum of the content
of sodium salt and potassium salt adds up to 100 %,
[0082] as well as an ion exchange in an exchange bath comprising
between 0 wt % and 10 wt % of a sodium salt, preferably sodium
nitrate NaNO.sub.3, in relation to the total amount of the salt,
for a period of time of at least one hour and at most 6 hours at a
temperature of the exchange bath of at least 380.degree. C. and at
most 440.degree. C., whereby a potassium salt is added to the
exchange bath, in particular preferably potassium nitrate
KNO.sub.3, in particular such that the sum of the content of sodium
salt and potassium salt adds up to 100 wt %, as well as,
optionally, one further exchange step or a plurality of further
exchange steps.
[0083] As already explained above, this means that, insofar as an
ion exchange of sodium for lithium takes place, that is, an ion
exchange in an exchange bath comprising between at least 20 wt %,
and up to 100 wt % of a sodium salt, this occurs as a first step.
However, this step is merely optional, that is, need not
necessarily be carried out.
[0084] Necessary, however, is the step of an ion exchange of
potassium for sodium, that is, in an exchange bath comprising
between 0 wt % and 10 wt % of a sodium salt, preferably sodium
nitrate NaNO.sub.3, in relation to the total amount of the salt,
whereby a potassium salt is added to the exchange bath, in
particular preferably potassium nitrate KNO.sub.3, in particular in
the form that the sum of the content of sodium salt and potassium
salt adds up to 100 wt %.
[0085] A further aspects relates thus to a glass article, produced
or producible in a method according to embodiments of the present
disclosure and/or comprising a glass according to the third aspect
of the disclosure.
[0086] A yet further aspect of the disclosure is directed towards a
use of the glass article according to embodiments, as a cover
panel, in particular as a cover panel for devices in consumer
electronics, in particular for display devices, monitors for
computing devices, measurement devices, TV-devices, in particular
as cover panel for mobile devices, in particular for at least one
device of the group comprising: mobile terminals, mobile data
processing devices, such as mobile phones, mobile computers, palm
tops, laptops, tablet computers, wearables, portable watches and
time measuring devices, or as a protective glass, in particular as
a protective glass for machines, or as a glazing in high-speed
trains, or as safety glass, or as automobile glazing, or in diving
watches, or in submarines, or as a cover panel for
explosion-protected devices, in particular for those in which the
use of glass is mandatory.
EXAMPLES
[0087] An exemplary range of composition of a glass is given by the
following composition in wt %:
TABLE-US-00003 SiO.sub.2 57 to 69, preferably 59 to 69, especially
preferred 61 to 69, where the upper limit in each case can be
preferably 67, Al.sub.2O.sub.3 17 to 25, preferably 17 to 24,
especially preferred 17 to 21, B.sub.2O.sub.3 0 to 7, preferably 0
to 5 especially preferred 0 to 4.5, Li.sub.2O 3 to 5.5, preferably
3.5 to 5.5 especially preferred 3.5 to 5, Na.sub.2O 0.8 to 6,
preferably 0.8 to 5.5, especially preferred 0.8 to 4.5, K.sub.2O 0
to 1, preferably 0 to 0.8, especially preferred 0 to 0.7, MgO 0 to
2, preferably 0 to 1.5, especially preferred 0 to 1, CaO 0 to 4.5,
SrO 0 to 2, preferably 0 to 1.5, especially preferred 0 to 1, ZnO 0
to 3, preferably 0 to 2, especially preferred 0 to 1.5,
P.sub.2O.sub.5 0 to 3, preferably 0 to 2, especially preferred 0 to
1.7, ZrO.sub.2 0 to 3, preferably 0 to 2.8, especially preferred
0-2.5 and most especially preferred 0 to 1, where, furthermore,
contaminants and/or refining agents and/or coloring constituents
can be present in amounts of up to 2 wt %.
[0088] FIG. 1 is the schematic and not dimensionally accurate
illustration of a plate-shaped glass article in accordance with the
presently disclosed embodiments.
[0089] FIG. 2 shows a schematic and not dimensionally accurate
sectional illustration of a glass article 1 in accordance with the
presently disclosed embodiments. In this case, the glass article 1
has two zones 101 that are arranged on the two main surfaces of the
glass article and are under compressive stress and may also be
referred to as zones of compressive stress. These zones of
compressive stress 101 have the dimension "DoL," likewise drawn
schematically in FIG. 2. For reasons of simplicity and clarity of
the illustration, zones of compressive stress at the lateral edge
of the main surfaces, which may be present there and may extend
perpendicular to the main surface, are not illustrated in the
figures. It is possible that the DoL on the two sides of the
plate-shaped glass article differ in terms of their size, whereby,
however, these differences lie, as a rule, within the limits of the
measurement accuracy, so that the DoL for a plate-shaped glass
article 1, is the same on both sides--at least within the limits of
measurement accuracy.
[0090] Between the zones of compressive stress 101, there lies the
region 102, which is under tensile stress.
LIST OF REFERENCE NUMBERS
[0091] 1 plate-shaped glass article
[0092] 101 zone of compressive stress
[0093] 102 inner region of the glass article under tensile
stress
* * * * *